The proposed conference is the 18th in a series of Gordon Research Con- ferences that originated in 1966 with a conference on cardiac muscle. The major focus of the 1989 conference will be: The molecular basis of the contractile process. The purpose of this conference is to summarize the major areas of progress during the past 3-5 years, and to point the way to those areas which should provide productive research in the immediate future. The work to be presented will deal with mammalian skeletal, cardiac and smooth muscles as well as with selected non-muscle contractile systems. In the past three years significant progress has been made in a broad range of areas in muscle research. Particular emphasis will be given to new methods involving genetics and molecular biology to discover the relationship between the amino acid sequence of the contractile proteins, their three-dimensional structures and their enzymatic and mechanical activity. The ability to produce site-specific mutations in actin genes and to then assess the effect of these mutations in living fibers has been achieved. Functional myosin heads have been cloned and expressed and can now also be analyzed using the powerful tools of molecular genetics. A high resolution crystal structure of G-actin has been completed and promises to aid in defining the structure of F-actin filaments. The myosin subfragment-1 head has also been crystallized and progress toward solving the structure of these crystals will be presented. The force on single actin filaments has been measured providing a new tool for studying the contractile interaction. Spectroscopic probes have been placed on the neck region of the myosin head, which is the portion of the head most likely to undergo rotations during contraction. A major theme will be the correla- tion of biochemical information from purified systems with similar studies in skinned muscle fibers. New photolabile precursors of nucleotide analogs allow kinetic experiments in fibers to focus on specific chemical reaction steps. The conference will include a limited number of formal presenta- tions with emphasis being placed on discussion and informal interchanges. Ample use will be made of poster presentations and discussion of this material will be incorporated into the main program. This conference has become a major triennial meeting which attracts the leading investigators in muscle research from around the world.